JPH07114462B2 - Auto focusing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an autofocusing method used for various video cameras and the like.

(Prior Art) Conventionally, attention has been paid to the fact that the voltage level of the high frequency component of a video signal obtained by photographing a subject corresponds to the definition of the reproduced image, and the voltage of this high frequency component is gain controlled. After that, the focus voltage is taken out as shown in FIG. 5, and the focus lens is driven so that the focus voltage becomes the maximum level, thereby performing the focusing so that the position of this lens coincides with the just focus position. Are known.

And, such a focusing system is known as a so-called hill climbing servo system, and this system is NHK Technical Research Report Sho. 40, Vol. 17, No. 1, Vol. 86, page 21, or Showa. It is explained in detail in the literature such as the Technical Report of the Television Society published in November 1957, ED No. 675.

Further, as such an autofocus system, the just focus position is detected by detecting a coincidence point between the focus voltage En detected along with the movement of the focus lens and a preset reference voltage value SEn. .

That is, for example, as shown in FIG. 3, when the reference voltage value SEmax that matches the focus voltage Emax is at the same level twice in succession, the intermediate position between the two detection positions is the just focus position. become.

Therefore, in the autofocus system, focusing can be performed by controlling the movement of the focus lens so as to be located at the intermediate position.

(Problems to be Solved by the Invention) For the reason of the circuit structure, it is preferable to control the gain so that the focus voltage is within a predetermined level range as shown by the alternate long and short dash line in FIG.

However, if the gain is reduced, the change in the focus voltage in the vicinity of the just focus position becomes gradual, which increases the return amount M in focusing.

Further, even when the same subject is photographed, focusing is regularly performed at regular intervals.

Then, when the return amount M becomes larger than the depth of field of the focus lens, there is a problem that a blurred state is repeatedly generated with a constant interval.

(Means for Solving Problems) The present invention has been made in view of the above circumstances, and by reducing the return amount in the vicinity of the just focus position, an autofocus that does not cause a blurring state due to focusing is generated. It is intended to provide a singing method.

In order to achieve this object, the present invention uses a gain control means 10 to gain a predetermined high frequency component of a video signal obtained by shooting a subject by a control amount obtained according to the input level. After that, the detection means 11 sequentially extracts the focus voltage En for each predetermined period, sequentially compares these focus voltages En with a plurality of reference voltage values set in advance by the control means 3, and compares these. It is an auto-focusing method that performs focusing by moving the focus lens 1 in the optical axis direction based on the result, and the difference between the respective reference voltage values obtained based on these comparison results is calculated as follows. Provided is an autofocusing method characterized in that the return amount M in the vicinity of the just focus position is made smaller by making it smaller than the larger one. It is intended.

(Operation) According to the autofocusing method as described above, when the gain in the gain control becomes large, that is, the focus voltage
When the change of En becomes sharp, the difference H between the reference voltage values SEn becomes large.

On the other hand, when the gain is reduced, that is, the focus voltage
When the change of En becomes gentle, the difference H between the reference voltage values SEn also becomes small.

Therefore, even if the gain is reduced, the focus voltage En and the reference voltage value
The return amount M determined at the intersection of SEn can be made smaller than in the conventional example.

(Embodiment) A preferred embodiment of the present invention will be described in detail below with reference to FIGS. 1 to 4.

FIG. 1 is a block diagram showing the configuration of an autofocus device for realizing the autofocusing method according to the present invention. The autofocus device includes an afocal lens 5 and a focus lens (master lens) 1. The optical system 6 is provided.

Focusing is performed by moving the focus lens 1 in a predetermined direction (arrows A and B directions) in the optical axis direction by a pulse motor 2 which is a moving unit in the present embodiment. 1 is moved simultaneously with the start of focusing. The position of the focus lens 1 on the optical axis is detected by a rotary encoder provided in the pulse motor 2 and is used as position information SS _{1 by the} control means. It is supplied to a certain microcomputer 3 (hereinafter, referred to as the microcomputer 3).

Further, the imaging light from the subject that is incident through the optical system 6 as described above is the CCD that is the imaging means in this embodiment.
It is photoelectrically converted into an electric image signal S ₂ by the image pickup device 7 using a (charge coupled device) or the like.

Then, the video signal S ₂ is amplified by an amplifier 8 and supplied to a camera circuit (not shown) and the like, and is also supplied to a bandpass filter (BPF) 9. The bandpass filter 9 outputs the video signal S ₂ from the video signal S _2. A predetermined high frequency component is extracted and supplied to the gain control circuit (GC) 10.

Then, the gain control circuit 10 controls the gain so that the high-frequency component falls within a predetermined level, and then supplies the high-frequency component to a detector (DET) 11, which detects the image. A focus voltage En as shown in FIG. 2 corresponding to a predetermined high frequency component of the signal S ₂ is obtained.

The gain control by the automatic gain control circuit 10 is performed based on the gain control signal S ₃ supplied from the microcomputer 3, and the microcomputer 3 responds to the level of the focus voltage En supplied as described later. Then, the gain is appropriately varied, and when the level of the focus voltage En reaches the saturation level Nmax, the gain control signal S ₃ that drops to the minimum value level Nmin is output.

The focus voltage En is the A / D (analog-digital) converter 1
It is digitized in 2 and supplied to the microcomputer 3.

Then, the microcomputer 3 sequentially samples the focus voltage En accompanying the movement of the focus lens 1 in the optical axis direction for each field from the start of focusing.

The microcomputer 3 also stores a plurality of reference voltage values SEn (n is a natural number) and a unique number (corresponding to n) for each reference voltage value SEn.

Then, the difference H of the reference voltage value SEn is increased or decreased in accordance with the gain control signal S _3.

That is, when the gain is large, the difference H is increased as shown in FIG. 2, and when the gain is small, the difference H is also decreased.

The difference H is naturally larger than the amplitude level of noise in the circuit.

Then, the microcomputer 3 sequentially compares the levels of these reference voltage values SEn with the focus voltages detected as described above,
When they match, only the number unique to the matched reference voltage value is read.

Here, the microcomputer 3 stores the magnitude relationship between the numbers unique to each reference voltage value, and when the newly read number is larger than the number read previously, the focus lens When it is determined that 1 has not reached the just focus position P, the control signal S ₄ that keeps moving the focus lens 1 is supplied to the motor drive circuit 13.

In this way, the autofocus device according to the present embodiment is
It is possible to read out a unique number for each reference voltage value SEn and continue moving the focus lens 1 based only on this number. Therefore, in the case where the differential voltage of each focus voltage is actually smaller than the detection limit value. Even if there is, reliable focusing can be performed.

On the other hand, the microcomputer 3 takes in the position information S ₁ indicating the position xn of the focus lens 1 at this time when the focus voltage En of the same level as each reference voltage value SEn is detected.

In the present embodiment, the focus voltage is taken into the microcomputer 3 as discrete information for each field. Therefore, in this embodiment, the captured value is the reference voltage value SE.
Assuming that the focus voltage En detected when n is first exceeded has reached the reference voltage value SEn, the focus voltage E at this time
n and the position information S ₁ are taken in.

In addition, in the autofocus device as described above, the third
As shown in the figure, when the unique number is detected twice in succession in the reference voltage value SEmax that is taken as the maximum reference voltage value SEmax is reached, the just focus position P is detected in these two times. It will be in the middle of the position.

Therefore, when the same number is read twice, if the focus lens 1 is moved to an intermediate position between the two detection positions, the position of the focus lens 1 coincides with the just focus position P. Can be made.

Therefore, in such a case, the microcomputer 3 moves the focus lens 1 in the opposite direction (arrow B direction) to the position information S ₁
By supplying a control signal S ₄ for moving the motor by a predetermined amount based on the above, the pulse motor 2 is rotated in the opposite direction to perform focusing.

On the other hand, as shown in FIG. 4, when the number read out as described above is at a level smaller than the number read out before, the detected position before that is the just focus position P. .

Therefore, in such a case, the focus lens 1
Can be made to coincide with the just focus position P by returning to the previous detection position.

Also in this case, the microcomputer 3 is used as in the case described above.
Supplies a control signal S ₄ for moving the focus lens 1 in the opposite direction to the motor drive circuit 13 for focusing.

As described above, according to the present embodiment, the difference H between the reference voltage values SEn is set smaller in accordance with the gain control signal S ₃ in the smaller control amount than in the larger control amount. The return amount M, which is determined by the intersection of the focus voltage and the focus voltage, is set particularly when the gain control amount in the gain control circuit 10 is small.
It can be made smaller than the conventional example.

As a result, it is possible to prevent the occurrence of a blurring state due to focusing.

In the present embodiment, a unique number is stored in each reference voltage value SEn, but each reference voltage value is stored in place of this number.
A code unique to SEn may be stored.

(Effects of the Invention) As is apparent from the above description, the present invention reduces the difference between the reference voltage values particularly when the gain control amount is small, so that the focus lens of the focus lens in the vicinity of the just focus position is reduced. The amount of return can be reduced.

As a result, it is possible to prevent occurrence of a blurring state due to focusing.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment according to the present invention, FIG. 2 is a graph showing a focus voltage, FIGS. 3 and 4 are graphs showing a relationship between a focus voltage and a reference voltage value, respectively. 6 is a graph showing the relationship between the focus voltage and the reference voltage value in the conventional example. 1 ... Focus lens, 2 ... Pulse motor, 3 ...
Microcomputer, 10 ... Gain control circuit.

Claims (1)

[Claims] 1. A detection means 11 after a gain control means 10 controls a gain of a predetermined high frequency component of a video signal obtained by photographing an object by a control amount obtained according to an input level thereof. The focus voltage En is sequentially taken out at every predetermined period, and these focus voltages En are sequentially compared with a plurality of reference voltage values set in advance by the control means 3, and the focus lens 1 is determined based on these comparison results. An auto-focusing method in which focusing is performed by moving in the optical axis direction, and the difference between the reference voltage values obtained based on the results of these comparisons is made smaller when the smaller control amount is compared to the larger one. Thus, the autofocusing method is characterized in that the return amount M in the vicinity of the just focus position is reduced.